The development of Gravitational Wave (GW) astronomy has gone hand in hand with a thriving interest in Primordial Black Holes (PBHs). The first observation of a binary black hole (BBH) merger [1]} has been shown compatible with scenarios in which PBHs constitute an appreciable fraction or even all of the cold dark matter (CDM) [2]}, [3]}, [4]} and subsequent GW observations has uncovered tantalizing mysteries that may hint at the existence of PBHs. For example, the existence of compact objects in the so-called mass gap and the observed low effective spin of the mergers are features that can be hardly explained if black holes are of stellar origin, but are in perfect agreement with (and possibly predicted by) the PBH scenario [5]}, [6]}, [7]}. Some scientists even believe the recent common-spectrum process observed by NANOGrav [8]} could also be a sign of PBHs [9]}, [10]}, [11]}.
